"At this point, this trickle of mammals into South America stopped for tens of millions of years, and the resulting isolation produced many peculiar South American forms – as isolation always does. The radiation among the Xenarthra produced the lumbering, elephant-sized ground sloths and the spectacular and seemingly-Mesozoic glyptodonts – giant armored armadillos, as big as a small car, with spikes along their tails. The caviomorph rodents also flourished, leading to the capybara, porcupines, chinchilla, guinea pigs, and the now extinct “Ratzillas” -- Phoberomys pattersoni, a bison-sized guinea-pig like creature, and its close relative, Josephoartigasia monesi, which weighed a metric ton and is the current record-holder for largest rodent ever. Some sizable predators evolved as well -- the sabre-toothed panther-like marsupial, Thylacosmilus (“pouch sabre”) and the giant flightless terror birds, the phorusrhacids, some of which stood as large as ten feet tall. These birds did not become extinct until just a few million years ago and had they lived until the present day, it is likely the notion that birds evolved from dinosaurs would have occurred to biologists much earlier. The surprising size of a number of the South American plant-eaters was probably an effective enough adaptation against the relatively small number of predators there, so they remained slow and untroubled. "Thus, up until a few million years ago, South American flora and fauna were quite as distinctive as the Australia and New Zealand biota seem today – and just as vulnerable. But, in one of those colossal transformational episodes that so often grips this world, the Isthmus of Panama emerged from the sea, and South America suddenly became acquainted with the cunning, speed, teeth, and claws of the Laurasian biotic realm. As noted, biogeographers refer to the event as an “interchange,” as plants and animal moved in both directions between the continents. But it is certainly clear that North America had the upper hand. Perhaps, the most obvious result we find in the fossil record is that North American meat-eaters flooded southward into this new-found rich and fleshy landscape and discovered a wealth of large and lumbering herbivores to rend and claw. As the biologist Stephen Wroe described it, “At that point, suddenly, wham, the carnivore diversity in South America goes absolutely stratospheric… You go from having a handful of not particularly big mammalian carnivores to having arguably the most extraordinary range of big carnivores in the world." These predators include massive sabre-toothed cats, bears, at least six species of canines, and a 400 kg lion that was four times larger than the marsupial lion. The gargantuan sizes attained by relatives of the South American guinea pigs, armadillos, and sloths would not have been enough to protect them from the northern marauders. And the rise of the Panamanian link may be properly described as a South American disaster, not as devastating as the one that befell their Antarctic relatives, but certainly far gorier. It produced what perhaps was the bloodiest spectacle since the fall of the tyrannosaurs....

Excerpt from Chapter Five:

"The Bloody Fall of South America...."

Glyptodont – giant armored armadillo

Some of the unique South American animals that evolved during the continent's isolation from 35 million years ago to just a few million years ago: